The objectives are to elucidate hypothalamic regulation of AP function, with particular emphasis on control of prolactin, GH, LH, FSH and TSH. Particular emphasis will be given to the possible role of neurotransmitters in the hypothalamus on AP function. During different physiological states (pre-puberty, estrous cycle, castration, positive feedback by gonadal hormones on gonadotropin release, stress, aging, lactation, pregnancy, etc.), hypothalamic concentration and turnover of biogenic amines and other neurotransmitters will be measured and compared against anterior pituitary hormone levels in the circulation. The neuroendocrine mechanisms responsible for the inverse relationship between prolactin and gonadotropin release will be studied, as well as the mechanisms responsible for the negative and positive feedback of gonadal hormones on secretion of gonadotropins. Studies on the relation of the neuroendocrine system to reproductive senescence and to development and growth of mammary and pituitary tumors also will be continued.